1. Field of the Invention
The invention relates to a method for selectively removing a sacrificial material on a substrate and, more particularly, to a method for selectively assisting the decomposition of the sacrificial material using ultraviolet (UV) radiation.
2. Description of Related Art
As is known to those in the semiconductor art, interconnect delay is a major limiting factor in the drive to improve the speed and performance of integrated circuits (IC). One way to minimize interconnect delay is to reduce inter-connect capacitance by using low dielectric constant (low-k) materials as the insulating dielectric for metal wires in the IC devices. Thus, in recent years, low-k materials have been developed to replace relatively high dielectric constant insulating materials, such as silicon dioxide. In particular, low-k films are being utilized for inter-level and intra-level dielectric layers between metal wires in semiconductor devices.
Additionally, in order to further reduce the dielectric constant of insulating materials, material films are formed with pores, i.e., porous low-k dielectric films. Such low-k films can be deposited by a spin-on dielectric (SOD) method similar to the application of photo-resist, or by chemical vapor deposition (CVD). Thus, the use of low-k materials is readily adaptable to existing semiconductor manufacturing processes.
Furthermore, in yet another attempt to reduce the dielectric constant of insulating materials, air gap structures are contemplated. Air gap structures are formed by depositing a sacrificial material on a substrate and then depositing a bridging material over the sacrificial material. Thereafter, at a later point in the device manufacturing process, the sacrificial material is decomposed and removed in order to leave a gap or void in its absence. Conventionally, the sacrificial material is removed using a chemical or thermal process.
However, despite the promise of superior electrical performance by this approach, the mechanical stability is a primary concern. In particular, when the bridging materials, which may include porous low-k materials, are formed across wide spaces, these materials have been observed to collapse during decomposition and subsequent process steps. Furthermore, the selection of a sacrificial material, the selection of a bridging material, and the processes for preparing, forming and integrating these materials pose numerous challenges for the successful implementation of an air gap structure in an IC device.